The point is, conditions can present differently in different groups of people, and can have different causes, when exclude major swaths of the population in testing you are leaving more blind spots and less trust in the medical system as a whole for many.

Autistic women and to some extent other minorities are notoriously under diagnosed because the original study only focused on white boys. There have been more studies but the damage has been done and many doctors even now are still withholding valid diagnosises based off of faulty research.